Thermosetting resins such as phenol resins, melamine resins, epoxy resins, unsaturated polyester resins, and bismaleimide resins are based on thermosetting properties and are excellent in water resistance, chemical resistance, heat resistance, mechanical strength, and reliability. Accordingly, thermosetting resins have come to be widely used in various industrial fields.
However, phenol resins and melamine resins have drawbacks in that volatile byproducts are generated during hardening, epoxy resins and the unsaturated polyester resins have a drawback of poor flame retardancy, and bismaleimide resins have a drawback of very high cost.
In order to overcome the drawbacks, there has been studied polybenzoxazine obtained by performing a ring-opening polymerization reaction on a benzoxazine ring, which leads to thermosetting, without the generation of volatile matter, which is considered to be a problem.
To obtain a thermosetting resin having a benzoxazine ring in the molecular structure thereof, an oxazine ring is opened by heating and polymerization is performed without the generation of byproducts. Accordingly, the thermosetting resin having the benzoxazine ring is receiving attention as a thermosetting resin for use in an encapsulant, an impregnating agent, a laminate, an adhesive, a paint, a coating material, a friction material, FRP, and a molding material. Such a benzoxazine ring has a complex structure including benzene and oxazine rings.
Polybenzoxazines are hardened polymers having a high glass transition temperature (Tg), low permittivity, high tension, a low coefficient of thermal expansion, excellent elasticity, and low hygroscopicity, thus maintaining a balance between mechanical, electrical, and chemical properties.
Techniques for further enhancing the properties of benzoxazines have been continuously developed. For example, Korean Laid-Open Patent Application No. 10-2012-0058566 relates to a “polybenzoxazine composition”, and discloses a method of preparing polybenzoxazine having favorable thermal stability, the method including heating a hardenable composition including a benzoxazine compound and a pentafluoroantimony acid catalyst at a sufficient temperature for a sufficient time to thus achieve polymerization.
Further, Korean Patent No. 10-0818254 relates to “a polybenzoxazine-based compound, an electrolyte membrane including the same, and a fuel cell using the same”, and discloses a novel polybenzoxazine-based compound having improved acid trapping performance, mechanical and chemical stability, and ability to retain phosphoric acid at high temperatures, an electrolyte membrane using the same, and a method of preparing the same.
Meanwhile, a copper clad laminate (CCL) is a laminate with a thin copper foil on an insulating material. In accordance with the recent high performance and high integration of smart devices, a copper clad laminate used in a printed circuit board (PCB) is required to have excellent heat resistance and low permittivity. A resin is used as the base material of the copper clad laminate, and serves as an insulator in the printed circuit board. Permittivity must be low in order to form an excellent insulator. Permittivity refers to the degree of polarization of molecules in a nonconductor relative to an external electrical signal. The smaller the permittivity, the better the insulating performance. As the permittivity of the insulator is reduced during the operation of the printed circuit board, the processing speed of the signal is increased and transmission loss is reduced.
As an alternative to satisfy the requirements for heat resistance and low permittivity of the above-described copper clad laminate, the use of polybenzoxazine, which is a phenol-based hardening agent, has been emphasized. As described above, polybenzoxazine is a thermosetting polymer obtained by polymerizing a benzoxazine-based monomer while a ring is opened in a molecule of the monomer by heat. Polybenzoxazine can be self-hardened without byproducts, does not generate volatile materials, and is not changed in terms of volume during hardening, thus ensuring excellent dimensional stability. Further, polybenzoxazine is a highly heat-resistant polymer having a high glass transition temperature and decomposition of less than 1% at thermal decomposition temperatures of up to 350° C.